全文获取类型
收费全文 | 2333篇 |
免费 | 117篇 |
国内免费 | 8篇 |
专业分类
2458篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 56篇 |
2021年 | 114篇 |
2020年 | 70篇 |
2019年 | 58篇 |
2018年 | 108篇 |
2017年 | 79篇 |
2016年 | 99篇 |
2015年 | 147篇 |
2014年 | 176篇 |
2013年 | 208篇 |
2012年 | 196篇 |
2011年 | 176篇 |
2010年 | 108篇 |
2009年 | 106篇 |
2008年 | 112篇 |
2007年 | 107篇 |
2006年 | 103篇 |
2005年 | 64篇 |
2004年 | 53篇 |
2003年 | 44篇 |
2002年 | 33篇 |
2001年 | 10篇 |
2000年 | 9篇 |
1999年 | 11篇 |
1998年 | 14篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1969年 | 3篇 |
排序方式: 共有2458条查询结果,搜索用时 15 毫秒
141.
Expression of transmembrane carbonic anhydrase isoenzymes IX and XII in normal human pancreas and pancreatic tumours 总被引:1,自引:1,他引:0
Kivelä AJ Parkkila S Saarnio J Karttunen TJ Kivelä J Parkkila AK Pastoreková S Pastorek J Waheed A Sly WS Rajaniemi H 《Histochemistry and cell biology》2000,114(3):197-204
Carbonic anhydrase (CA) IX and XII are transmembrane isoenzymes which are expressed in several epithelia and overexpressed in some carcinomas. They have recently been linked to von Hippel-Lindau gene-mediated carcinogenesis in that both isoenzymes are downregulated by the product of the wild-type von Hippel-Lindau tumour suppressor gene. This paper describes the localisation of CA IX and XII in the normal human pancreas and pancreatic tumours. Both isoenzymes showed positive reaction in the basolateral plasma membrane of the normal acinar and ductal epithelia. The hyperplastic ductal epithelium in tumour specimens generally showed an increased staining for CA IX. Of 29 malignant tumours of exocrine pancreas, 10 showed moderate or strong immunoreaction for CA IX. The signal for CA XII remained weak in most malignant lesions. The present results show that both CA IX and XII are unevenly expressed in the ductal and acinar compartments of the human pancreas. The expression of these isoenzymes in a relatively low number of malignant tumour specimens suggests that they have a limited value in diagnostic evaluation of pancreatic carcinoma. However, the increased expression of CA IX in hyperplastic ductal epithelium may contribute to the pancreatic tumourigenesis. 相似文献
142.
Son Radu Shahilah Abdul Mutalib Gulam Rusul Zainori Ahmad Tadaaki Morigaki Norio Asai Yung Bu Kim Jun Okuda Mitsuaki Nishibuchi 《Applied microbiology》1998,64(3):1153-1156
Twelve strains of Escherichia coli O157:H7 were isolated from 9 of 25 beef samples purchased from retail stores in Malaysia. These strains produced Shiga toxin 2 with or without Shiga toxin 1 and had the eae gene and a 60-MDa plasmid. The antibiograms and the profiles of the arbitrarily primed PCR of the strains were diverse, suggesting that the strains may have originated from diverse sources. 相似文献
143.
144.
Asharaf Abdul Salam Ibrahim Elsegaey Rshood Khraif Abdullah AlMutairi Ali Aldosari 《PloS one》2015,10(5)
The Arab world, which consists of the 22 member states of the Arab League, is undergoing a rapid transition in demographics, including fertility, mortality, and migration. Comprising a distinctive geographic region spread across West Asia and North East Africa and unified by the Arabic language, these states share common values and characteristics despite having diverse economic and political conditions. The demographic lag (high fertility and low mortality) that characterizes the Arab world is unique, but the present trend of declining fertility, combined with the relatively low mortality, brings about significant changes in its population size. This research aimed to: (i) assess the population growth in the Arab world over 3 time periods, (ii) explore its components, and (iii) understand its public health impact. Data from the International Data Base (IDB) of the U.S. Census Bureau for 3 time periods (1992, 2002, and 2012) in 21 countries of the Arab world were analyzed by dividing them into four geographic sectors, namely, the Gulf Cooperation Council (GCC), West Asia, Maghreb, and the Nile Valley African Horn. The population of the Arab world has grown considerably due to both natural growth and migration. The immigration is pronounced, especially into resource-intensive GCC nations, not only from East Asian and Central African countries but also from resource-thrifty (limited-resource) Arab nations. The migrations within, as well as outside, the Arab world reveal an interesting demographic phenomenon that requires further research: migration flows and trends. However, the transformations in public health statistics related to mortality—the impact of demographic changes—depict a new era in the Arab world. 相似文献
145.
Wetlands are sensitive ecosystems that are increasingly subjected to threats from anthropogenic factors. In the last decades, coastal Mediterranean wetlands have been suffering considerable pressures from land use change, intensification of urban growth, increasing tourism infrastructure and intensification of agricultural practices. Remote sensing (RS) and Geographic Information Systems (GIS) techniques are efficient tools that can support monitoring Mediterranean coastal wetlands on large scales and over long periods of time. The study aims at developing a wetland indicator to support monitoring Mediterranean coastal wetlands using these techniques. The indicator makes use of multi-temporal Landsat images, land use reference layers, a 50m numerical model of the territory (NMT) and Corine Land Cover (CLC) for the identification and mapping of wetlands. The approach combines supervised image classification techniques making use of vegetation indices and decision tree analysis to identify the surface covered by wetlands at a given date. A validation process is put in place to compare outcomes with existing local wetland inventories to check the results reliability. The indicator´s results demonstrate an improvement in the level of precision of change detection methods achieved by traditional tools providing reliability up to 95% in main wetland areas. The results confirm that the use of RS techniques improves the precision of wetland detection compared to the use of CLC for wetland monitoring and stress the strong relation between the level of wetland detection and the nature of the wetland areas and the monitoring scale considered. 相似文献
146.
Brendan Collins Simon Capewell Martin O’Flaherty Hannah Timpson Abdul Razzaq Sylvia Cheater Robin Ireland Helen Bromley 《PloS one》2015,10(6)
Background
Increasing evidence associates excess refined sugar intakes with obesity, Type 2 diabetes and heart disease. Worryingly, the estimated volume of sugary drinks purchased in the UK has more than doubled between 1975 and 2007, from 510ml to 1140ml per person per week. We aimed to estimate the potential impact of a duty on sugar sweetened beverages (SSBs) at a local level in England, hypothesising that a duty could reduce obesity and related diseases.Methods and Findings
We modelled the potential impact of a 20% sugary drinks duty on local authorities in England between 2010 and 2030. We synthesised data obtained from the British National Diet and Nutrition Survey (NDNS), drinks manufacturers, Office for National Statistics, and from previous studies. This produced a modelled population of 41 million adults in 326 lower tier local authorities in England. This analysis suggests that a 20% SSB duty could result in approximately 2,400 fewer diabetes cases, 1,700 fewer stroke and coronary heart disease cases, 400 fewer cancer cases, and gain some 41,000 Quality Adjusted Life Years (QALYs) per year across England. The duty might have the biggest impact in urban areas with young populations.Conclusions
This study adds to the growing body of evidence suggesting health benefits for a duty on sugary drinks. It might also usefully provide results at an area level to inform local price interventions in England. 相似文献147.
Ajit Kumar Ngangbam Abdul Baten Daniel L. E. Waters Steve Whalan Kirsten Benkendorff 《PloS one》2015,10(10)
Dicathais orbita is a marine mollusc recognised for the production of anticancer compounds that are precursors to Tyrian purple. This study aimed to assess the diversity and identity of bacteria associated with the Tyrian purple producing hypobranchial gland, in comparison with foot tissue, using a high-throughput sequencing approach. Taxonomic and phylogenetic analysis of variable region V1-V3 of 16S rRNA bacterial gene amplicons in QIIME and MEGAN were carried out. This analysis revealed a highly diverse bacterial assemblage associated with the hypobranchial gland and foot tissues of D. orbita. The dominant bacterial phylum in the 16S rRNA bacterial profiling data set was Proteobacteria followed by Bacteroidetes, Tenericutes and Spirochaetes. In comparison to the foot, the hypobranchial gland had significantly lower bacterial diversity and a different community composition, based on taxonomic assignment at the genus level. A higher abundance of indole producing Vibrio spp. and the presence of bacteria with brominating capabilities in the hypobranchial gland suggest bacteria have a potential role in biosynthesis of Tyrian purple in D. orbita. 相似文献
148.
Ifedayo M. O. Adetifa Abdul Khalie Muhammad David Jeffries Simon Donkor Martien W. Borgdorff Tumani Corrah Umberto D’Alessandro 《PloS one》2015,10(10)
Background
A Tuberculin skin test (TST) survey was conducted to assess the prevalence of latent TB Infection (LTBI) and to estimate the annual risk of M. tuberculosis infection (ARTI) in Gambian school children. The results are expected to contribute to understanding of Tuberculosis epidemiology in The Gambia.Methods
This was a nationwide, multi-cluster survey in children aged 6–11 years. Districts, 20 of 37, were selected by probability proportional to size and schools by simple random sampling. All TST were performed using the Mantoux method. Height and weight measurements were obtained for all participants. We calculated prevalence of LTBI using cut-off points of 10mm, the mirror and mixture modelling methods.Results
TST readings were completed 13,386 children with median age of 9 years (interquartile range [IQR] 8–10 years). Mixture analysis yielded a cut-off point of 12 mm, and LTBI prevalence of 6.9% [95%CI 6.47–7.37] and the ARTI was 0.75% [95%CI 0.60–0.91]. LTBI was associated gender and urban residence (p <0.01). Nutritional status was not associated with non-reactive TST or sizes of TST indurations. ARTI did not differ significantly by age, gender, BCG vaccination or residence.Conclusions
This estimates for LTBI prevalence and ARTI were low but this survey provides updated data. Malnutrition did not affect estimates of LTBI and ARTI. Given the low ARTI in this survey and the overlapping distribution of indurations with mixture modelling, further surveys may require complementary tests such as interferon gamma release assays or novel diagnostic tools. 相似文献149.
A number of penicillin derivatives (4a-h) were synthesized by the condensation of 6-amino penicillinic acid (6-APA) with non-steroidal anti-inflammatory drugs as antimicrobial agents. In silico docking study of these analogues was performed against Penicillin Binding Protein (PDBID 1CEF) using AutoDock Tools 1.5.6 in order to investigate the antimicrobial data on structural basis. Penicillin binding proteins function as either transpeptidases or carboxypeptidases and in few cases demonstrate transglycosylase activity in bacteria. The excellent antibacterial potential was depicted by compounds 4c and 4e against Escherichia coli, Staphylococcus epidermidus and Staphylococcus aureus compared to the standard amoxicillin. The most potent penicillin derivative 4e exhibited same activity as standard amoxicillin against S. aureus. In the enzyme inhibitory assay the compound 4e inhibited E. coli MurC with an IC50 value of 12.5 μM. The docking scores of these compounds 4c and 4e also verified their greater antibacterial potential. The results verified the importance of side chain functionalities along with the presence of central penam nucleus. The binding affinities calculated from docking results expressed in the form of binding energies ranges from -7.8 to -9.2kcal/mol. The carboxylic group of penam nucleus in all these compounds is responsible for strong binding with receptor protein with the bond length ranges from 3.4 to 4.4 Ǻ. The results of present work ratify that derivatives 4c and 4e may serve as a structural template for the design and development of potent antimicrobial agents. 相似文献
150.
Edmond Wonkam-Tingang Isabelle Schrauwen Kevin K Esoh Thashi Bharadwaj Liz M Nouel-Saied Anushree Acharya Abdul Nasir Suzanne M Leal Ambroise Wonkam 《Experimental biology and medicine (Maywood, N.J.)》2021,246(13):1524
Approximately half of congenital hearing impairment cases are inherited, with non-syndromic hearing impairment (NSHI) being the most frequent clinical entity of genetic hearing impairment cases. A family from Cameroon with NSHI was investigated by performing exome sequencing using DNA samples obtained from three family members, followed by direct Sanger sequencing in additional family members and controls participants. We identified an autosomal dominantly inherited novel missense variant [NM_001174116.2:c.918G>T; p.(Q306H)] in DMXL2 gene (MIM:612186) that co-segregates with mild to profound non-syndromic sensorineural hearing impairment . The p.(Q306H) variant which substitutes a highly conserved glutamine residue is predicted deleterious by various bioinformatics tools and is absent from several genome databases. This variant was also neither found in 121 apparently healthy controls without a family history of hearing impairment , nor 112 sporadic NSHI cases from Cameroon. There is one previous report of a large Han Chinese NSHI family that segregates a missense variant in DMXL2. The present study provides additional evidence that DMXL2 is involved in hearing impairment etiology, and we suggest DMXL2 should be considered in diagnostic hearing impairment panels. 相似文献